Thickened lubricants



THICKENED LUBRICANTS Everett C. Hughes, Shaker Heights, and Ernest C.Milherger, Maple Heights, Ohio, assignors to The Standard Oil Company,Cleveland, Ohio, a corporation of Ohio No Drawing. Application October6, 1954 Serial No. 460,759

6 Claims. (Cl. 252-25) This invention relates to an aerogel grease ofgood high temperature stability and water resistance.

While the Word grease has usually been employed to describe an oilthickened with a soap, it is here used in a broader sense to include anythickened lubricant.

It is generally known that soap-base greases break down at hightemperatures, of the order of 300 to 400 F. This breakdown isaccompanied by an irreversible change in the grease structure, so thatupon cooling the grease is observed to have lost its grease-likecharacteristics. The aerogel greases usually are far superior to thesoap-base greases in stability at high temperatures as the followingtable shows:

breaks down late a heavy liquid.

However, after heating at high temperatures some aerogel greases tend tolose consistency upon stirring. This is undesirable because there aremany field applications where a grease is agitated or worked Whilesubject to a high temperature and it is important that the grease retainits consistency under these conditions and subsequent thereto.

Accordingly, it is the object of the present invention to provide anaerogel grease having improved stability at high temperatures,particularly after working at high temperatures.

In accordance with the invention, these objects are accomplished byincorporating a water-miscible or watersoluble polyhydric alcohol in anaerogel grease composition comprising a lubricating oil thickened with anonabrasive, inorganic thickening or gelling agent, and particularlyfinely divided silica, a silica aerogel being illustrative. Thickenedlubricants so prepared have excellent temperature susceptibilityproperties.

The grease is also rendered more or less resistant to deterioration bywater by incorporating a hydrophobic cationic surface-active waterstabilizer therein in the form of Amine O, 1-fl-hydroxyethylZ-heptadecenyl imidazoline.

The presence of the polyhydric alcohol in an amount to obtain improvedhigh temperature stability does not markedly affect the consistency ofthe thickened lubricant, i. e., the amount of the inorganic gellingagent to impart a given consistency to the thickened lubricant is notmaterially modified. Furthermore, the inclusion of atent Patenteddan.21, 1958 the polyhydric alcohol will not effect a change in theconsistency of the thickened lubricant upon storage. The

polyhydric alcohol likewise does not affect the water-' thickenedlubricant has excellent storage stability. This is to be contrasted withthe heat susceptibility and deterioration of fatty materials insoap-base greases.

The preparation of the grease is simple and readily adaptable tocontinuous operation, as contrasted with the involved grease-makingtechniques which are often considered in the industryas an art.

The oil stock used in making the thickened lubricant may be widelyvaried, as contrasted with present greasemaking requirements in whichthe oil in many cases must meet certain critical specifications.

In addition, the avoidance of the use of soap permits the manufacturerto be independent of the fat supply, which is important in periods inwhich fats and soaps are scarce and, many times, of pronouncednon-uniformity.

The inorganic gelling agent to be used in making the thickened lubricantin accordance with this invention may be any inorganic material whichforms a gel with a lubrieating oil and which is so finely divided as tobe nonabrasive. The preferred materials are the aerogels, which may beformed from any material not, incompatible with oil, such as silica,alumina, and other gel-forming metal oxides.

A series of silica aerogels which can be used as the inorganic gellingagent of the invention are marketed under the trade name Santocel.

Santocel C is prepared from a sodium silicate solution in the followingway: The solution is neutralized with sulfuric acid and then allowed tostand until the mixture sets to form a hydrogel. The by-product sodiumsulfate is washed out by the repeated washings with water. Thecontinuous water phase in this hydrogel is then replaced by continuedwashing with alcohol untilan-alcogel is formed. In order to remove theliquid phase without a collapse of the gel structure, the alcogel isplaced in an autoclave which is then heated above the criticaltemperature of the alcohol and the pressure is allowed to increase to apoint above the criticalpressure of the alcohol. The vent valve is thenopened and the alcohol allowed to escape. Under these conditions, thesilica gel structure remains practically undisturbed and the liquidphase of the gel is replaced with air. The material is then reduced inparticle size by blowing it through a series of pipes containing sharpbends with jets of compressed air. Santocel C has a secondaryagglomerate particle size of about 3 to 5 microns.

Santocel A is prepared as set forth for Santocel C up to the point ofremoval of the product from the autoclave. This material is run througha continuous heating chamber where it is heated for /2 hour to atemperature of about 1500 F. to eliminate the last traces of volatilematerial. It is then broken down in a reductionizer or micronizer to aparticle size of about hi inch in diameter. The solids content of theoriginal hydrogel used in preparing Santocel C is approximately 25higher than that of Santocel A.

AR is a modification of A, differing only in that the.

CDv is a C which has been devolatilized as set forth. for A. CDv isreductionized before being devolatilized.

CDvR differs slightlyfr'om CDv in that the CDvR has beendevol'a'tilizedjust after heating in the autoclave andthenreductionized. It differs-from CDv in that the latter is reductionizedbefore being devolatilized.

The primary dilierences, between the and the :Qs.

areas follows}. i

Q(.-1) Thev Cs. are prepared .from a sodiunif. silicatejsolutioncontaining 25 more silica, than, the Afs. "There? fore, in general the.As. are lighter and; composed/of smaller particles than theCs.

2) T.h .-Ash ve. undergone adevolatiliiatibn'step'in their preparation.i

The following are the bulkldensities a preferred silica" sm ele l V p Y,Densitngrams perm. AR 7 9.029 RD: 0.05am 0.064 P g 0.082

In general; AR and AR D -show superior-gelling ability and the As ingeneral are better'tha-n'dhee Gs Silica aerogels which havebeendevolatilized generally have a higher gelling eificiency than-theundevola-tilizedaerogels.

. Other types of'inorga-nic gelling agents which maybe used'inelude aFumed Silica; ltzis finely divided and appears very much like anaerogel. It is made by acornbu'stion' or vaporization process, asa-Lsource oh white carbon black for the rubber inclustryz -The particlesare several microns in size and porousib nature.

Another material is" Linde Silica Flour! It is-very similar in-physicalappearance-to the silica aerogel. Theparticle-size of" the silica ispurported-to be-050l 'to-0;05' micron and-to be manufactured byburningsilicon tetrachloride and collecting the combustion productoncoolplatesanalogous totheproductionof carbon-blacl The particles are thoughtto be aggregates orclusters' of'particles rather than ofsponge-hlecharacterr 1 1 Still'another'inorganijc gelling agentknown isiLudox silica which is known asa silica sol; and silicaderivativesthereotz It has a particle size ofthe order of 0:01" to 0.03micron. e

In preparing thickened lubricantsit'is' necessary to remove the waterfromthe sol and: replace it with an oil; Tl'llSlS' possible byformulating the lubricant and removing the water by flash distillationorazeotropic distillation;

No attempt is made to enumerate all of the inorganic gellingagents whichwill be suitable, norto present'exsamples of all of them since the novelaspects of'the invention reside in imparting highv temperature stabilityto the lubricant rather. than the use of novel; gelling agents, per se.f

The lubricating oilto be used in the processinay have any'lubricatingviscosity. It may be raw'oil, acid-refined, or solvent-refined; asrequired for the particular lubricating need. i

The nature of the base oil hasjbeen found to make little, difference inthe relative consistencies of the thickened' lubricants andconventionally (acid) *refined oils produce slightly thicker lubricantsthan solvent-refined oils. Excellent working stability is obtainedregardless of the type of the base oil. An increase in, theviscosity ofthe base oil, as might be expected, brings increased viscosity to: thethickened lubricant and minimizes-bleeding. The change is relativelysmalrand fairly linear. The viscosity 0f the. oil doesnot aiiect theWorking stabilityof the lubricant;

I The relative. proportions ofthe inorganic gelling agent and the oilwill vary somewhat dependingupon the desired body in the thickenedlubricant, the 'gelli'ngfabiiity oi the inorganic gelling agent andtheviscosity of the oil used. It has been noted, for instance, that withthe Linde Silica Flour, the lubricants are somewhat harder, i; e.,'

have a lower penetration than lubricants containing the same weight ofSantocel'. Lubricants made with low viscosity-oils. require a somewhatlarger amount of the inorganic gelling agent to git/ea lubricant of thesame penetration. The thickened lubricant may vary in consistency fromthe consistency of a'slightly thickenedoil to a solid or semi-solid of"grease-like consistency. In generahthe amount of the inorganic gellingagent falls within the range of 5 to 20%, and in most. cases would fallwithin the range of Ito-12%.

The amount of the inorganic gelling agent, as might be expected,afi'ects the'cons'istency offthe thickened t lubricant in that anincrease, in itsconcentration brings a corresponding.increaseeidconsistency. The' ralnge is In general, the. properties ofthe thickenedlubricants are remarkably independentof the compositionvariables. and are: not critical. The relative concentration of thegelling agentfefiects the mo-st' significant alteration particularlywithregardito the final consistency of the productf This permits, thernanufacture of thickened lubri cants hayinga wide variety ofconsistenciesf i A wide; variety of Water-nus ible orWater-sOIubZepOly-Q hydricfalcoholscan be: employedin accordance withthe. invention to; improve the. highqtemperature stability ofaerogel-base greases." Alcohols which are Water-immiscible, i. e., areoleaginoustin character, cannot be used, because they are hydrophobic.The alcohol must be hydrophilic, i. e., not oleaginous, for reasonswhich will be apparent from the theory of the; action of the alcohol,set forthlater...

Provided the polyhydric alcohol is thydrophilic, itmaya have from 2 to 8carbon atoms andmust contain at. least.

two hydroxyl groups. It may contain as. manyfa'sflfour.

hydroxyl groups, those having two. and, three hydroxyl' groups beingmost: available and Qt'hereforezbeing preferred: Other polargroups, suchas one or more ether or amino' groups, may also bepresent." The twoandthree-hydroXyl' polyhydric alcohols are employed-in the examples becauseof their low cost and availability. The polyhydric alcohol may containother inert substituents, such as halogen,- which have been found not toreduce the activity of the compounds.

of the invention, are ethylene glycol, diethylene, glycol;

glycerol a-monomethyl ether, glycerol, dulcitol; erythritol;pentaerythritol, mannitol, sorbitol, glycerol: chlorohydrin, l-rnethyl,glycerol; trirnethylene. glycol, butandiol-ZJ;

pinacol, propylene glycol, butantriol, and polymeric dihyt droxy-.(glycol): .polyetherederived; by condensation; of e ethyleneoxideorupropyleneoiddm containingifrom twoto.

ten, oxide units;

The polyhydric alcohol need not be oil-soluble,- -but shonldbe.oili-dispersible: f litshonldihave a: minimumboilingpointofiabout :6.since it'sprima'ry'purposeis to stabilize the. grease atahightemperatures. I a

The 'polyhdric alcohol: ist-incorporated in the aerogel-" 7 base.gnease'imam amount toimpart high; temperature 7 stability. Ordinarily:a=concentrationof polyhydric alco= hol'. ranging-from 0.25 to about 1%byweight ofthe aerogel-base grease givessatisfactory results. There isno reason to employ more polyhydric alc'ohol than' isknecessary; butexcessiveamounts do no harm, and amounts" up to 5% or even-higher havebeensuccessfullyemployed; The amount "of hydrophobic-- cationicsurface-'active agent to impart water-resistance to theaerogel greasejinthe form, of l -B7hydroxylethyl2 heptadecenyl iinida z olihe willvaryfrom 0:1% to about 5%, depending-upon ;th" water-stabilizing efiect'desired, the amount andfinaturef of" the gelling agent fused,.and theeconomics involved" In S'OI'IlBil'lSlfillCCS, the compositioncontainingth pol hydric alcohol high temperature stabilizermay not disi-'Exempli-iying compounds within the. scope;-

play a long life when used continuously at high temperatures. Abreakdown in high temperature stability at high temperatures if itappears is due to a decomposition,

through oxidation, of the polyhydric alcohol stabilizer of theinvention. In such circumstances, it is desirable to include in thecomposition an antioxidant for the polyhydric alcohol stabilizer.Conventional amine antioxidants which are more readily oxidized than thepolyhydric alcohols of the invention can be employed for this purpose.Tetramethyldiamiuodiphenylmethane is a particularly desirableantioxidant for the polyhydric alcohols of the invention. Only smallquantities are required, and ordinarily an amount ranging from 0.1 toabout 1% by weight of the aerogel base grease is ample. There is noreason to employ more antioxidant than is necessary to produce thedesired effect, but excessive amounts do no harm and amounts up to 5%can be used, if desired.

The composition is made simply by mixing the inorganic gelling agent,the oil, a polyhydric alcohol and the cationic water stabilizer in anyorder or manner.

In one embodiment, the polyhydric alcohol and the cationic waterstabilizer, can be incorporated with the inorganic gelling agent eitherby mixing directly or, if desired, by dissolving them in a solvent,mixing the solution with the gelling agent and evaporating the solvent.

Generally, the polyhydric alcohol and cationic water stabilizer aredispersed in the oil and the inorganic gelling agent added thereto andmixed therewith. Any simple mixing technique can be employed and, ifdesired, the

mixture can be homogenized in a colloid mill, although this is notnecessary.

The composition of the invention is not limited to the oil, gellingagent, cationic water stabilizer, and polyhydn'c alcohol. Any of thematerials conventionally added to lubricants and greases may beincluded. The expression consisting essentially o as used herein isintended to refer to the components which are essential to thecomposition, namely, the oil, the inorganic gelling agent and thepolyhydric alcohol, and the expression does not exclude other componentsfrom the composition which do not render it unsuitable for lubrication,such materials being, for instance, the cationic water stabilizer, highpolymers to modify viscosity or viscosity index, materials to imparttackiness, lubricating solids such as graphite, antioxidant additives,corrosion inhibitors of various types, sulfur, additives, to render thelubricant suitable for use in gears, for cutting, grinding, etc.

The following examples illustrated preferred embodiments of theinvention. In the examples, water-resistant thickened lubricants areprepared to show the absence of an etfect of the polyhydric alcohol onthe water resistance of the grease.

Examples 1 to 6 The base grease used in Examples 2 to 6 was a commercialwater-resistant aerogel grease of the following formulationSolvent-extracted neutral oil (250 SSU at 210 F.) 85.98

1 (l-B-hydroxyethyl-2-heptadeceny1-imidazpline) An isobutylene polymersold by the Emmy Company, Inc. and commonly usecl in nomnoundinggreases.

A FriedeI-Crat'ts reaction product. useful as a pour point depressantand sold by the Enjay Company, Inc. v

This base grease is referred to hereafter as the Aerogel W. R. BaseFormula (Example 2). One of the poly- .hydric alcohols listed in thefollowing table, in the amount stated in the table, was incorporated inthis g'ia's'e, by blending it with the oil, and then mixing in the othercomponents of the grease (Examples 3 to 6). The resulting greasecompositions were tested for high temperature stability by measurementof micropenetrations before and after heating to 400 F. The resultsobtained were compared with the results for the base grease formulationabove, and also with non-water-resistant aerogel grease containing 10%Santocel C and No. 250 solvent-extracted neutral oil which did notcontain Amine 0 (Example 1). Thisformula is referred to hereinafter asthe Aerogel Base Formula.

The grease is prepared for the determination of high temperaturestability by placing approximately cc. of grease in a 150 ml. beaker.The beakers are heated to the test temperature by placing them in analuminum block furnace. This furnace consisted of a solid block ofaluminum heated 'by internal electrical heaters. Six holes, each largeenough to accommodate a 150 cc. beaker, were drilled in the top of theblock, together with a thermocouple, so that a measure of thetemperature of the block could be obtained. In this manner, six beakerscould be heated simultaneously. The beakers containing the grease wereplaced in the aluminum furnace and held there until the equilibriumtemperature of the grease was 400 F. The samples were stirred atfive-minute intervals during heating. After this the grease was allowedto cool to room temperature overnight and then was stirred vigorouslywith a spatula.

Kaufman micropenetration measurements were obtained on the grease beforeand after the testprocedure (Industrial and Engineering Chemistry,Analytical Edition, volume 11, page 108, 1939), and theresults areexpressed in the table below as percent increase in penetration.

The following results were obtained on the aerogelbase greases tested,containing the polyhydric alcohols listed in the amounts stated:

TABLE II Added Percent Increase After Original' Block None (Aerogel 243Base Formula). None (AerogelW.

R. Base Formu- Soup la). Glyccrlne .do

Ethylene Glycol--.

The results show that an aerogel-base grease which does not containAmine O in order to improve its water stability (Example 1) has a hightemperature stability which while superior to soap types leaves much tobe desired. When Amine O and other components are added to this basegrease (Example 2) the stability at 400 F. is destroyed and the greaseliquefies, and remains liquid after cooling. Through addition ofglycerine and ethylene glycol in amounts ranging from 0.5 to 1%, theeffect of the Amine O is completely overcome and the aerogel greasepossesses a better high temperature stability than the original AerogelBase Formula.

Examples 7 to 12 Aerogel greases were prepared by blending a poly vhydric alcohol into the base oil and subsequently mixing thiscomposition with Santocel and the other-ingredients aerwas geod.

to prepare ilie grease. frheseigreasesfihad the following(l-heptadeceny1-2-B-hrrlroxyethyldmidazoline.) k

' 'An isobutylenc'polymersold by theEnjayCompany, In'c.

"andic'omjm only used ir' compounding greases. v

A Friedel-Crafrs reaction product. usefuLas a pounpoint depressant-and;soldby heEnjay Company, Inc.

' Specifications for Petroleum Products. The cone and grease cupemployed in obtaining the "following 'test results'require'd aminimumsample "size of 35 'rn'l.

"TABLE III.-- -MICR O CONE DIMENSIONS -AS'[-M 801110 Cone Cup -Cone CupDiameter, mm 65 78 43 Height, mm-" 45 17 Depth, mm Surface, sq.'mm.-Volume, cc Cone, diam .lcnp Surfam Cone. height/cup depthwtnot'assembly, gms (ealcd) wt. of assembly/sq. mm. cone 0. 021 0. 021

"surface.

'The following results were obtained:

" iTABLEl-IV I 801110 Micropenetrations Ex. f3 No. SantocelA'ddit-ivelPercent Used) v 1 Origi-. -'=After Percent E nal Block.Increase 7 AR I 0.5%GlyceroL; 99 122 p 23 124 (87). ('12) 8 AR'P 1.0%Glycerol 9a 112 19. 2 9 "AR" 0;5%Ethylenc Glycol"; '90 125 39 (117) 10..AR:v LOVE/Ethylene Glycol... 1465 11'.-. ARE.- N0ne I 120 188 -5(i.51'2. "'KRD" 1.0% Glycerol 20 It will be noted that the. greasecontaining glycerol and Santocel ARD (Example 12")Ih'a's :a" better hightemperature stability than the corr sponding grease (Example .11) whendid nofcontain fglyc'erol. The high ,tenfiperature station 5116f thegreases containinga'pblyhydrie alco- 8 Examples 1370-16 'A-n aerogelwater-resistant 'grease ofthe 'followinglforfmulawas .made up:

LAY

. Percent *SantocelARD Amine 40M Paratac 2 Y 'Paraflow 3 Methane BaseBright Stock (78 SUS at 210 -F.) Polyhydric-alcohol- :p'olyhydricalcoholin accordance with the-invention (and reducing the brightstock'according'ly) in order "toprepare an aerogelgrease which is "notonly water-resistant but also stablelat'high temperatures. a

In. preparing these greases;tthe Aminefo and'the poly- :hydric alcoholto be tested were dissolved; in a stock solutionofthe baseoilfcontaiuing the other componentsL The Santocel was added to this.solution and'completely wetted by stirring. 'The grease Was'preparedat95 'FJbymiXing .for the time indicated in the following table, thetimebeing varied so as to approximate the final penetration: of 'thetaerogelwater-resistant base formula. lfthis time is thesame as or longer and/orif the :original penetration is the same as or less ,thanthat of thebase formula,l"it is evident that the'polyhydric alcohol-has either no:onfa

The "penetration ofthe grease .wastaken "beforeand :after-heating-intheblock described in Example 1, imac- =cordance with theShell,-Microcone'Penetration vTest"(-Institute Spokesman (NLGI) volume-VI,=.Number.12, page TABLE V 'High Temperature Stability Mixing Tmmed VNo. Additive ime, Shell 7 i 'Shell' Stabil- Minutes Pen. Il'o.Penetration Lity cles "Initial 'Flnal 13"; Ae'rogel'Base 7 40 159 '5 157Q02- None.

Formula. 14..-. Aerogel W. R. 30 159 4 171 '267 Good.

Base Formula. 15--.- Ethylene 20 159 4 167 201 Do.

Glycol. A 16.." Glycerol 30 5' 168 "205 D0.

Same formula as Example 1.

The results show that incorporating the Amine (Twin .the aerogel baseformula appreciably increasesthepenetration and thus reduces the hightemperature:stability. This eflcct of the Amine O is, however, overcome.by

the polyhydric alcohols added to the aerogel waterrresistant baseformula.

Examples 17' to '26 I "Microcone Penetration lest before andafterheatizrg in Company, Inc. and

9 the aluminum block to 400 F. The following results were obtained:

Same as formula in Example 1.

These data show that increasing the amount of glycerol beyond 2% has noappreciable effect upon the high temperature stability, although it doesno harm. in each case the ethylene glycol and glycerol overcome theeffect of the Amine O on the high temperature stability of the aerogelgrease, and in Examples 21, 22, 23 and 26 the high temperature stabilityis improved, compared to the original Base Formula (Example 17).

Examples 27 I 37 A large number of aerogel greases were prepared asfollows: A fixed quantity of oil (78 SSU at 210 F. solvent-extractedbright stock) was weighed out into a 400 ml. beaker. 0.8% Amine O wasadded, and 1% of the alcohol additive was incorporated in the base oil.The oil mix, was heated to 130 F. while being mixed with a Lightninstirrer, and 8% Santocel ARD was mixed in with hand stirring. Theresulting grease Was allowed to stand overnight. An original penetrationwas then obtained using the Shell Microcone Penetration Test and thegrease was then subjected to the block test. Grease samples exhibitingsome degree of high temperature stability were cycled three or fourtimes. Each sample was tested also for water stability and given avisual rating for consistency while at 400 F.

The alcohol additives tested included monohyclric and polyhydricalcohols. Ethylene glycol and glycerol were included to evaluate theresults obtained. Data from these tests are given in the followingtable:

TABLE VII Block" Test Ex. Shell Penetrations Water No. AdditiveStability Orig. 1 2 3 4 Aerogel W. R. Base For- 139 200 226 Good.

mula.

Monohydric Alcohols 27--.. 2-Ethylhexanol 128 290 Do. 28---. Laurylalcohol. 135 Do. 29.-.. 5 Ethylnouanol 156 D0. 30 HeptadecanoL. 128 Do.31--.. Cetylalcohol 126 298 Do.

- Polyhydric Alcohols 32...- Diethylene glycol 135 178 180 195 130.33.... Triethylene glycoL. 127 179 186 190 195 Fair. 34.". Ethyleneglycol.... 114 139 165 184 184 Good 35 Pentanediol-l,5 146 186 197 Do.36.... Glycerol... 130 147 l58 168 173 D0. 37.... Trimetliylol propane.154 I 194 i 194 207 I"... Do.

Without exception, the five monohydric alcohols tested wereunsatisfactory under high temperature conditions The initialpenetrations for ethylene glycol, diethylene glycol, triethylene glycoland glycerol are lower than that of the control grease, and indicatethat these compounds have no deleterious effect on grease yield. All ofthe polyhydric alcohols tested exert a stabilizing effect at hightemperatures.

Examples 38 and 39 Additional greases were prepared from a blend ofbright stocks to produce an oil of approximately 2000 SSU at F. Hightemperature instability of aerogel greases is aggravated when a heavybase oil is used, and thus this provides a severe test of the hightemperature stabilizing effect of the additives of the invention.

The test greases were prepared as outlined in the preceding Examples 27to 37. The results are given in the following table:

It is evident that the polyhydric alcohols are capable of increasinghigh temperature stability, even when a heavy base oil is employed.

Examples 40 to 44 Percent Percent Santocel O 10.0 10.0 Amine O L 1.0 1.0Paratac 2. 0 2. O Paraflow 0. 5 0. 5 Methane base 0.5 0.5 Red dye. 0. 02O. 02 Glycol 0. 5 to 1. 0 Solvent-extracted neutral oil (250 SSU at 100F.) 85. 98 84. 98 to 85. 98

1 l-B-hydroxyethyl-2heptadecenyl-imidazoline.

2 An isubutylene polymer sold by the Enjay Company, Inc. and commonlyused in compounding greases.

3 A Frledel-Gral'ts reaction product, useful as a pour point depressantand sold by the Enjay Company, Inc.

4 Tetramethyldiaminodiphenylmethane.

The base grease used in Examples 41 to 44 was the commercialwater-resistant aerogel grease of Formula A. This base grease isreferred to hereafter as the Aerogel W. R. Base Formula (Example 41). Toprepare Examples 42 to 44, one of the glycols listed in the followingtable, in the amount stated in the table, was incorporated in thisgrease by blending it with the oil, and then mixing in the othercomponents of the grease. The resulting grease compositions were testedfor high temperature stability by measurement of micropenetrationsbefore and after heating to 400 F. as in Examples 1 to 6. The resultsobtained were compared with the results for the W. R. base greaseformulation above, and also with non-water-resistant aerogel greasecontaining 10% Santocel. C and 9.0% No. 250 solvent-extracted neutraloil which did not contain Amine 0 (Example 40). This latter formula isreferred to hereinafter as the Aerogel Base Formula. 0

The results show that an aerogel-base grease which does not containAmine O in order to improve its water stability (Example 40) has a hightemperature stability which, while superior to soap types, leaves muchto be desired. When Amine O andother components are added to this basegrease (Example 41) the stability at 400 F. is destroyedand the greaseliquefies, and remains liquid after cooling. Through addition ofdiethylene glycol in amounts ranging from 0.5 to 1%, the effect of theAmine O is completely overcome and the aerogel grease possesses a betterhigh temperature stability than the original Aerogel BaseFormula.Polyethylene glycol 900 also overcomes the effcct of the vAmine 70 onhigh temperature .stability.

Example 45 Aerogel water-resistant greases of the followingl-fl-hydroxyethyl-Zhcptadecenyl-imidazollne. ZrAn isobutylene polymersold by the Enjay Company, Inc. and commonly used in compoundinggreases.

3A Friedel-Cratts reaction product, useful as a pounpoint depressant andsold by the Enjay Company, Inc.

4 letramethyldiaminodiphenylmethane.

Example 45 is the water-resistant Formula A modified .by addition of.l%. diethyleneglycol-inaccordance-with the invention "(and reducing thebright. stock accordingly) 'inorder to prepare an aerogel greasewhichisnot only water-resistant but also-stable at high temperatures.

In preparing these greases, the Amine O and the glycolto be.tested.weredissolved in a stocksolution of thebase. oil containing'theothercomponents. .ThefSantoeel was added to this. solution andcompletely wettedby stirring. The-grease was ,prepared at9'5 .by' mixingfor the time "indicated-in" the followingtable, the time being variedsoas to approximate 'the -final penetration of "the aerogelwater-resistant base formula. If thistime is'the same as or longerand/or if the: original penetrait is:;evident;that the ether has eitherno ora Lben'eficial effect on yield. The penetration of the greasewastaken before and after heating in the block described in accordancewith the Shell Microcone Penetration Test (Insti i tute Spokesman NLGI),VI, 12, page 1 1943)).

TABLE X High Temperature f Stability Mixing Immed. Time, Shell Min- Pen.utes Water Sta- 'Shell Penetrability.

Ex. N o. Additive tion No. Cycles 7 Initial Final Formula'A Diethyleneglycol.

Good.-

130. Do. i

aws- The results .show that the Amine O in 'Formu1a-A appreciablyincreases the penetrationand thus reduces the high temperaturestability. This efiect of the Amine O is, however, overcome by theglycol'(Ex'ample 45).

Examples 46 to 48 A number of aerogel greases were prepared-.ofthefollowing formulations:

Santocel ARD Amine 0 Paratac Parafiow, 3 s Methane base (Oalco MB)Bright stock (78 SSU-at210 F.) Glycol 1 1-,3-hydroxyethyl2-heptadecenylimidazoline.

2 An isobutylene polymer sold by the En ay Company, Inc.;and commonlyused in compounding greases.

3 A Friedel-Orafts reaction .prod uct,..useful as-a pourpoint-depressant and sold by the Enjay Company, Inc. V p vTetramethyldiaminodiphenylmethane.

Formula A is Example 46 inthetable whichltollows;

Formula B is the water-resistantformula ofFormula. A, :modified byadditionof '.1-% glycol .inaccordance with the invention, reducing thebright stock accordingly in order to prepare an aerogelgreasewhichis-notsonly water-resistant but also stable athightemperatures- .In preparing thesegreases, the Amino O 1and-theglycol to be tested-were dissolved in -a stock-solution of the base oilcontaining the other components. The

Santocel was added to the solution and completely wetted tion isthe-same as or less'than that of the base-formula, following resultswere obtained:

TABLE'XI i k Biock"-test, Shell Pens. Water =Ex. "Additive Per- Pen.Stabil- ENO- cent Cycle Eity 3 IOrig. 1st 2nd 3rd 4th -16---Controlwith1inine0 v139 e00, .226 43.5" iC ood. i

DjfethylenesglycoLn u- 1:0 17s use .197 -15 .Do.

Polyethylene glycol 400..-. 1.0 159 I198 "39 Do.

The results show that incorporating the glycol in the control grease(containing Amine but no glycol) appreciably increases high temperaturestability, as ev 1- denced by a reduction in penetration increase. TlJlSis best observable in the change in penetration per cycle noted in theabove table. Diethylene glycol is most effective, but even thepolyethylene glycol 400 gives a significant improvement in hightemperature stability.

in the examples, the high temperature stability of the aerogel greasesis tested by heating the greases to 400 F. This is an extreme test,inasmuch as the highest temperature to which a grease is subjected undereven extraordinary conditions of use is about 300 F., but it was adoptedas a suitable test standard by which to measure the high temperaturestability of the greases because a grease stable at 400 F. willdefinitely have the stability necessary to withstand heating to 300 F.It will be understood that for normal purposes an aerogel grease neednot be stable at temperatures above about 300 F., and that the greasesof the invention at least meet this requirement. Where the term hightemperature stability is used, it will be understood to mean that theaerogel grease is stable at at least 300 F.

The following hypothesis is given as a partial explanation of the reasonto which is attributed the action of the polyhydric alcohol in improvingthe high temperature resistance of aerogel grease, but the invention isnot to be bound thereby.

Silica aerogels are known to be in the form of an extremely finelydivided material and it is thought that it is capable of forming acolloidal structure in the oil vehicle employed in an aerogel grease.Mixing or stirring in formulating the grease serves to disperse thesecondary aerogel agglomerates throughout the body of the oil. Theaerogel occupies a greater volume than the liquid oil vehicle, andbecause of this it is probable that the colloidal structure is aidedsomewhat by a close packing of the solid silica gel particles, perhapswith mechanical interlocking. It is thought that the basis of thestructure is a tying together of the various silica aerogel particles byhydrogen bonding between hydroxyl groups which remain attached toindividual silicon atoms in the silica gel molecule.

In setting up the colloidal grease structure, it is postulated that thedistances between adjacent hydroxyl groups on different particles ofsilica aerogel may be too great in some circumstances to form a binding,attractive force between particles. In this e ent, Water, which isalways present in the aerogel structure, serves to bridge the gapbetween adjacent particles through hydrogen bonding be tween thecompound and the hydroxyl groups on the adjacent silica aerogelparticles. Thus the water in effect aids in setting up the colloidalgrease structure, and may also link it together, at least in part.

When the grease under static conditions is submitted to temperatureshigh enough to volatilize the water no apparent effect is noticed atfirst, for there is no force to disarrange the structure. Consequently,penetration vs. temperature curves indicate that aerogel greases haveexcellent high temperature performance with a very low in crease inconsistency as the temperature is increased. However, when this staticstate is disturbed by stirring, the structure can and does collapse, dueto the absence of the water which has been volatilized and whichformerly served as the connecting links between adjoining silicaparticles. In consequence, the structure passes from a gel state to acolloidal sol state. This explains why the transformation of the heatedaerogel grease from a greaselike condition to a soupy condition occursonly after stirring and Why stirring thus brings about an apparentlyirreversible gel-to-sol transformation. This transformation may bereversed to some extent by adding Water to the soupy grease, tending tosubstantiate this hypothesis, but it is not possible to return thegrease to its original condition.

Thus, on the basis of this hypothesis, incorporation in the grease, inaccordance with the invention, of a polyhydric alcohol which is notvolatile at the temperatures to which the grease may be subjected leadsto a partial or complete displacement of Water in the aerogel bypolyhydric alcohol, possibly before and in any event at the time Wateris volatilized at an elevated temperature. The low volatility of thepolyhydric alcohol prevents its loss during heating and thus preventsdestruction of the colloidal grease structure when the aerogel grease isstirred after it has been heated to high temperatures. It is alsoapparent from this that a hydrophobic polyhydric alcohol which isimmiscible with Water could not function in this Way because it couldnot act as a substitute for Water in the hydrophilic gel structure.

This application is a continuation-in-part of our applications SerialNos. 119,752, filed October 5, 1949, 253,984, filed October 30, 1951,and 254,633, filed November 2, 1951, all three now abandoned.

We claim:

1. A water-resistant thickened lubricant of good temperaturesusceptibility properties, consisting essentially of a minerallubricating oil of lubricating viscosity, an inorganic gelling agentimparting a grease-like consistency to the oil upon addition thereto,1-/3-hydroxyethyl-2-heptadecenyl imidazoline imparting stability againstdeterioration by water, and a water-soluble polyhydric alcohol impartinghigh temperature stability.

2. A water-resistant thickened lubricant of good temperaturesusceptibility properties in accordance with claim 1 wherein thepolyhydric alcohol is glycerol.

3. A water-resistant thickened lubricant of good temperaturesusceptibility properties in accordance with claim 1 wherein thepolyhydric alcohol is ethylene glycol.

4. A water-resistant thickened lubricant of good temperaturesusceptibility properties in accordance with claim 1 wherein thepolyhydric alcohol is diethylene glycol.

5. A water-resistant thickened lubricant of good temperaturesusceptibility properties in accordance with claim 1 wherein thepolyhydric alcohol is triethylene glycol.

6. A water-resistant thickened lubricant of good temperaturesusceptibility properties in accordance with claim 1 wherein thepolyhydric alcohol is trimethylol propane.

References Cited in the file of this patent UNITED STATES PATENTS2,531,440 Jordan Nov. 28, 1950 2,554,222 Stross May 22, 1951 2,563,606Kimberlin et a1 Aug. 7, 1951 2,573,650 Peterson Oct. 30, 1951 2,662,056McCarthy Dec. 28, 1953 2,676,148 Iler Apr. 20, 1954 2,711,393 Hughes eta1 June 21, 1955

1. A WATER-RESISTANT THICKENED LUBRICANT OF GOOD TEMPERATURESUSCEPTIBILITY PROPERTIES, CONSISTING ESSENTIALLY OF A MINERALLUBRICATING OIL OF LUBRICATING VISCOSITY, AN INORGANIC GELLING AGENTIMPARTING A GREASE-LIKE CONSISTENCY TO THE OIL UPON ADDITION THERETO,1-B-HYDROXYETHYL-2-HEPTADECENYL IMIDAZOLINE IMPARTING STABILITY AGAINSTDETERIORATION BY WATER, AND A WATER-SOLUBLE POLYHYDRIC ALCOHOL IMPARTINGHIGH YEMPERATURE STABILITY.